Method for Producing a Connection Electrode for Two Semiconductor Zones Arranged One Above Another

ABSTRACT

A method for producing a connection electrode for a first and second adjacent and complementarily doped semiconductor zones includes a step of producing a trench extending through the first semiconductor zone into the second semiconductor zone in such a way that the first semiconductor zone is uncovered at sidewalls of the trench and the second semiconductor zone is uncovered at least at a bottom of the trench. The method also includes producing a first connection zone in the first semiconductor zone by implanting dopant atoms into the sidewalls at least at a first angle. The method further includes producing a second connection zone in the second semiconductor zone by implanting dopant atoms at least at a second, different angle. The method also includes depositing an electrode layer at least onto the sidewalls and the bottom of the trench for the purpose of producing the connection electrode.

This application is a divisional of U.S. application Ser. No.11/527,743, filed Sep. 26, 2006, which in turn claims the benefit ofGerman Application No. 10 2005 045909.9-33, filed Sep. 26, 2005.

BACKGROUND OF THE INVENTION

The present invention relates to a method for producing a connectionelectrode for two semiconductor zones which are arranged one aboveanother and are doped complementarily with respect to one another, inparticular a connection electrode for a source zone and a body zone of apower MOSFET.

In order to avoid negative effects of a parasitic bipolar transistorformed by the sequence of the drain or drift zone, the body zone and thesource zone in the case of a power MOSFET, it is known in the case ofpower MOSFETs to short-circuit the body zone and the source zone. Forthis purpose, a source electrode connected to the source zone isrealized in such a way that it also makes contact with the body zone andthereby short-circuits the source zone and the body zone.

In the case of so-called trench MOSFETs, in which the body zone and thesource zone are arranged in a manner lying one above another in asemiconductor body and in which gate electrodes are arranged in trenchesextending through the source zone and the body zone, it is known toarrange such a connection electrode in a trench extending into thesemiconductor region (mesa region) between two gate trenches through thesource zone right into the body zone.

SUMMARY OF THE INVENTION

In one exemplary embodiment of a method according to the invention forproducing a connection electrode for a first semiconductor zone and asecond semiconductor zone which are arranged one above another and aredoped complementarily with respect to one another, provision is madefirstly for producing a trench extending through the first semiconductorzone right into the second semiconductor zone in such a way that thefirst semiconductor zone is uncovered at sidewalls of the trench and thesecond semiconductor zone is uncovered at least at a bottom of thetrench. Afterward, a protective layer is applied to one of the first andsecond semiconductor zones in the trench and a first connection zone isproduced in the other semiconductor zone, which is not covered by theprotective layer. Said connection zone is produced by introducing dopantatoms into said other semiconductor zone via the trench. In this case,said dopant atoms are chosen such that a first connection zone ariseswhich is of the same conductivity type as said semiconductor zone notcovered by the protective layer, but is doped more highly. Afterward, anelectrode layer is applied to the sidewalls and to the bottom of thetrench in order to produce the connection electrode.

In the case of this method, the task of the protective layer is toprotect said one of the two semiconductor zones which is covered by theprotective layer, which semiconductor zone is referred to hereinafter asprotected semiconductor zone, against a doping by the dopant atoms whichare introduced into the other of the two semiconductor zones, which isreferred to hereinafter as unprotected semiconductor zone, via thetrench for the purpose of producing the first connection zone. It isnecessary to prevent said dopant atoms from being introduced into theprotected semiconductor zone because the dopant atoms used for producingthe first connection zone in the unprotected semiconductor zone arethose dopant atoms which produce a semiconductor zone of a complementaryconduction type with respect to the protected semiconductor zone. Saiddopant atoms would thus reduce the net doping of the protectedsemiconductor zone in the region of the trench, and thus reduce thecontact resistance between the connection electrode that is producedlater and said protected semiconductor zone.

In the case of this method, the protective layer itself may be a layercontaining dopant atoms, said dopant atoms being those dopant atomswhich produce a semiconductor zone of the same conduction type as theprotected semiconductor zone. The dopant atoms from said protectivelayer are indiffused into the protected semiconductor zone by at leastsaid protected semiconductor zone being heated to a predetermineddiffusion temperature for a predetermined time duration. As a result ofthis, a second connection zone, which is of the same conductivity typeas the protected semiconductor zone itself, arises in the protectedsemiconductor zone. The temperature during the thermal process and theduration thereof are dependent on the type of dopant atoms used.Diffusion processes of this type are sufficiently known, so that furtherexplanations in this respect can be dispensed with.

A first connection zone is produced for example by implanting dopantatoms into the unprotected semiconductor zone, that is to say thesemiconductor zone not covered by the protective layer, via the trench.After the implantation of the dopant atoms, a thermal step is required,as is known, by means of which the implanted region is heated to apredetermined temperature for a predetermined time duration in order toanneal irradiation damage caused by the implantation and to activate theimplanted dopant atoms, that is to say incorporate them into the crystallattice of the semiconductor material used. This thermal step foractivating the implanted dopant atoms may simultaneously be used as thethermal step for the indiffusion of the dopant atoms from the protectivelayer into the protected semiconductor zone. Depending on the type ofdopant atoms present in the protective layer and depending on the typeof implanted dopant atoms, however, it may also be necessary to carryout a thermal step as early as prior to the implantation of the dopantatoms for the purpose of producing the first connection zone, in orderthat the dopant atoms from the protective layer already partly indiffuseinto the protected semiconductor zone.

The protective layer with the dopant atoms present therein may comprisean electrically conductive material, such as, for example, dopedpolysilicon, or a dielectric material, such as, for example,arsenosilicate glass (ASG), phosphosilicate glass (PSG) or borosilicateglass. The type of doping of the polysilicon or the selection of one ofthe glass materials explained above is effected depending on whether ap-doped or n-doped second connection zone is intended to be produced bymeans of the diffusion process.

In this case, an electrically conductive protective layer may remainprior to producing the connection electrode in the trench, while adielectric, that is to say electrically insulating, protective layer hasto be removed after the production of the first and second connectionzones and prior to the production of the connection electrode.

A suitable protective layer is also a metal, such as, for example,titanium, which does not have a doping effect but which forms ametal-semiconductor compound with the surrounding semiconductor materialwhen the thermal step is carried out, and thus provides for alow-resistance connection contact. When using silicon as semiconductormaterial for the two semiconductor zones, a silicide forms when using ametallic protective layer in the transition region between saidprotective layer and the semiconductor material of the protectedsemiconductor zone, said silicide providing for a low-resistanceconnection contact. A suitable material for the protective layer istitanium, for example.

The protective layer may be applied to the first semiconductor zone inthe region of the sidewalls of the trench or to the second semiconductorzone in the region of the trench bottom.

The production of the first connection zone in the unprotectedsemiconductor zone not covered by the protective layer may also beeffected by means of a diffusion method by the application of a layercontaining dopant atoms in the trench at least onto the unprotectedsemiconductor zone and by the induffusion of dopant atoms from saidlayer into the unprotected semiconductor zone by means of a thermalprocess. In this case, the trench is preferably completely filled withthe material containing the dopant atoms.

One alternative to the method explained above consists in producing thetrench for the production of the connection electrode in two stages. Ina first step, the trench is produced down to a first depth, which issmaller than the trench depth ultimately desired. After this first step,a first connection zone is produced in the first semiconductor zone,which is uncovered at sidewalls of said trench. Said first connectionzone is produced for example by implantation of dopant atoms via thesidewalls of said first trench. The depth of said first trench may inthis case be chosen such that the first trench still ends within saidfirst semiconductor zone, but the trench may also already reach rightinto the second semiconductor zone. After the production of the firsttrench section, the trench is lengthened proceeding from its bottom inthe direction of the second semiconductor zone. Dopant atoms aresubsequently introduced via the bottom of the lengthened trench into thesecond semiconductor zone in order to produce a second connection zonethere. During the production of the first connection zone in the firstsemiconductor zone, that region of the second semiconductor zone inwhich the second connection zone is to be produced is protected againsta doping by the semiconductor section which is removed upon thelengthening of the trench in the direction of the second semiconductorzone.

A further alternative of the method according to the invention providesfor producing, after the production of the trench, the first connectionzone in the first semiconductor zone and the second connection zone inthe second semiconductor zone by implantation of dopant atoms, theseimplantation steps being effected at different implantation angleschosen such that sections of the second semiconductor zone remainomitted from a doping during the production of the first connection zonein the first semiconductor zone, and that sections of the firstsemiconductor zone remain omitted from a doping during the production ofthe second connection zone in the second semiconductor zone. Theproduction of the first connection zone in the first semiconductor zone,which is uncovered at sidewalls of the trench, is effected for exampleby implantation of dopant atoms at a first implantation angle chosensuch that the dopant atoms do not pass as far as the bottom of thetrench. The production of the second connection zone is effected forexample by implantation of dopant atoms at an angle of 0° relative tothe sidewalls of the trench, so that only dopant atoms are implanted viathe bottom of the trench into the second semiconductor zone during thisimplantation step.

What is common to all three methods explained above for producing aconnection electrode, which each comprise method steps for producing atleast one highly doped connection zone, is that during the production ofthe at least one connection zone in one of the two semiconductor zones,the other of the two semiconductor zones is protected against a doping.This protection may be effected by applying a protective layer, by meansof semiconductor sections that are initially present and are removed inthe further course of the method, or by suitably setting theimplantation angle during the implantation of dopant atoms.

BRIEF DESCRIPTION OF THE FIGURES

Exemplary embodiments of the present invention are explained in moredetail below with reference to figures.

FIG. 1 illustrates, on the basis of cross-sectional illustrations of asemiconductor body having a first and a second semiconductor zone, afirst exemplary embodiment of a method according to the invention forproducing a connection electrode, in which a protective layer is appliedto one of the two semiconductor zones, which remains on the respectivesemiconductor zone.

FIG. 2 shows a cross-sectional illustration of a semiconductor componentproduced by a modified method with respect to the method according toFIG. 1, in which the protective layer is removed.

FIG. 3 illustrates, on the basis of cross-sectional illustrations of asemiconductor body during different method steps, a second exemplaryembodiment of a method for producing a connection electrode, in which aprotective layer is applied to one of the two semiconductor zones.

FIG. 4 illustrates, on the basis of cross-sectional illustrations of asemiconductor body, a third exemplary embodiment of a method forproducing a connection electrode, in which the protective layer isapplied to one of the two semiconductor zones to be contact-connected.

FIG. 5 illustrates, on the basis of cross-sectional illustrations of asemiconductor body having a first and a second semiconductor zone to becontact-connected, a method for producing a connection electrode inwhich a trench for the connection electrode is produced in two stages.

FIG. 6 illustrates, on the basis of cross-sectional illustrations of asemiconductor body having a first and second semiconductor zone to becontact-connected, a method for producing a connection electrode forthese two semiconductor zones in which connection zones are produced inthe two semiconductor zones by means of implantation steps employingdifferent implantation angles.

FIG. 7 illustrates, on the basis of cross-sectional illustrations of asemiconductor body, a method for producing the trench for the connectionelectrode using a spacer produced by oxidation.

FIG. 8 illustrates a further method for producing a connection zone.

FIG. 9 illustrates a modification of a method step of the methodelucidated with reference to FIG. 8.

DETAILED DESCRIPTION OF THE FIGURES

In the figures, unless specified otherwise, identical reference symbolsdesignate identical component regions with the same meaning.

The methods according to the invention are explained below for theproduction of a connection electrode which makes contact with a sourcezone and a body zone of a power MOSFET or power IGBT and therebyshort-circuits these component zones. However, the methods according tothe invention are not restricted to this application, but rather can beapplied to the production of connection electrodes for arbitrarycomponents having two semiconductor zones which are arranged one aboveanother and are doped complementarily with respect to one another.

A first exemplary embodiment of a method according to the invention forproducing a connection electrode which makes contact with twosemiconductor zones doped complementarily with respect to one another,in which a protective layer is applied to one of the semiconductor zonesduring the method sequence, is explained below with reference to FIG. 1.

FIG. 1 a shows in side view a cross section through a semiconductor body100, in which a component structure for a power MOSFET is provided. Thiscomponent structure comprises a first semiconductor zone 11 arranged inthe region of a front side 101 of the semiconductor body, and a secondsemiconductor zone 12 adjacent to said first semiconductor zone 11 inthe vertical direction, said second semiconductor zone being dopedcomplementarily with respect to the first semiconductor zone 11. In thecase of a MOSFET or IGBT, the first semiconductor zone 11 forms thesource zone thereof and, in the case of a MOSFET or IGBT, the secondsemiconductor zone 12 forms the body zone thereof. The source zone 11 isn-doped in the case of an re-channel MOSFET, p-doped in the case of ap-channel MOSFET and usually n-doped in the case of an IGBT. The bodyzone 12 is in each case doped complementarily with respect to the sourcezone 11.

The second semiconductor zone 12 is arranged above a third semiconductorzone 13, which, in the case of a MOSFET and IGBT, forms the drift zone13 thereof and which is in each case doped complementarily with respectto the second semiconductor zone 12. A highly doped connection zone 14is adjacent to said third semiconductor zone 13 in the direction of arear side 102 of the semiconductor body 100 opposite the front side 101,which connection zone 14 forms the drain zone of the MOSFET or IGBT andis of the same conduction type as the drift zone 13 in the case of aMOSFET and is doped complementarily with respect to the drift zone 13 inthe case of an IGBT. This drain zone 14 may—as is illustrated by adashed line in FIG. 1 a—already be present prior to the production ofthe connection electrode yet to be explained. This connection zone 14may be for example a highly doped semiconductor substrate, to which thedrift zone 13, the body zone 12 and the source zone 11 are applied bymeans of an epitaxy method. However, the drain zone 14 may also beproduced for example by means of an implantation method, in which dopantatoms are implanted via the rear side 102 into the semiconductor body100, after the production of the connection electrode or duringimplantation steps yet to be explained during the production of theconnection electrode.

A gate electrode, two electrode sections 21 of which are illustrated inFIG. 1 a, extends in the vertical direction proceeding from the firstsemiconductor zone 11 through the second semiconductor zone 12 rightinto the third semiconductor zone 13 and is insulated from thesemiconductor zones 11, 12, 13 of the semiconductor body 100 by means ofa dielectric 22. In the direction of the front side 101, the gateelectrode is preferably covered by a thicker dielectric layer 23, whichalso extends in sections over the first semiconductor zone 11 above thefront side 101 of the semiconductor body. It should be pointed out inthis connection that the illustration of the layer thicknesses in thefigures is not true to scale. Thus, in particular, that section of theinsulation layer which extends over the first semiconductor zone 11 mayalso be embodied thicker than illustrated.

The aim of the method according to the invention is to produce aconnection electrode which makes low-resistance contact with the firstand second semiconductor zones 11, 12, but during the production ofwhich the doping concentrations of the first and second semiconductorzones 11, 12 is not altered in a region directly adjacent to the gatedielectric 22, since this would lead to a change in the electricalproperties of the trench MOSFET, in particular to a shift in thethreshold voltage.

In first method steps, the result of which is illustrated in FIG. 1 b,provision is made for producing a trench 15 in the mesa region betweentwo trenches having gate electrode sections 21 arranged therein, whichtrench extends through the dielectric layer 23 and the firstsemiconductor zone 11 right into the second semiconductor zone 12. Saidtrench 15 is arranged in a manner spaced apart in the lateral directionfrom the trenches having the gate electrode C sections 21. It should bepointed out that the production of the connection electrode is explainedbelow only with reference to one electrode section which is arrangedbetween two trenches having gate electrode sections arranged therein. Ina power MOSFET having a cell array having a multiplicity of gateelectrode sections 21 arranged in a manner spaced apart from oneanother, such connection electrodes are preferably produced in each mesaregion between two gate electrode sections 21.

The trench 15 has sidewalls 151 and a bottom 152. The firstsemiconductor zone 11 is uncovered at the sidewalls 151 of this trench15 after the production thereof. The second semiconductor zone 12 isuncovered at the bottom of the trench 152 and in sections also at thesidewalls of the trench 151 because the trench 15, proceeding from thefirst side 101, extends to below the interface between the first andsecond semiconductor zones 11, 12. The trench 15 is produced for exampleby means of a sufficiently known anisotropic etching method using a maskthat leaves the region of the trench free during the etching process.

In next method steps, which are illustrated in FIGS. 1 c and 1 d, aprotective layer 31 is produced in the trench 15, said protective layercompletely covering one of the two first and second semiconductor zones11, 12 within the trench. Referring to FIG. 1 c, for this purpose aprotective layer 31′ is deposited over the whole area, said protectivelayer covering the front side 101 of the semiconductor body 100 and alsothe side walls 151 and the bottom 152 of the trench 15. The depositionof said protective layer 31′ may be effected for example by means of aCVD method (CVD=chemical vapor deposition).

In next method steps, the result of which is illustrated in FIG. 1 d,said protective layer is removed at least from the bottom 152 of thetrench 15, thereby giving rise to a protective layer 31 at the sidewalls151 of the trench 15, said protective layer completely covering thefirst semiconductor zone 11 within the trench. The protective layer 31also covers in sections the second semiconductor zone 12 at thesidewalls of the trench, but leaves the second semiconductor zone 12free at the bottom of the trench 52. The production of said protectivelayer 31 at the sidewalls 152 of the trench is effected for example byanisotropically etching back the protective layer 31′. During thisanisotropic etching method, the protective layer 31′ is removed bothabove the front side 101 of the semiconductor body and from the bottomof the trench 152.

During next method steps, which are illustrated in FIG. 1 e, a firstconnection zone 16 is produced below the trench bottom 152 in the secondsemiconductor zone 12. Said first connection zone 16 is of the sameconductivity type as the second semiconductor zone 12, but doped morehighly. It is assumed for the explanation below that the firstsemiconductor zone 11 is doped with dopant atoms of a first conductivitytype, which are referred to hereinafter as dopant atoms of the firsttype, and that the second semiconductor zone 12 is doped with dopantatoms of a second conductivity type complementary to the firstconductivity type, which are referred to hereinafter as dopant atoms ofthe second type.

In order to produce the first connection zone 16, dopant atoms of thesecond type are implanted via the bottom 152 of the trench 15 into thesecond semiconductor zone 12. The thicker dielectric layer arrangedabove the gate electrode 21, which dielectric layer is also arranged insections above the first semiconductor zone 11 and extends as far as thetrench 15 in the lateral direction, during this implantation step 16,protects the first semiconductor zone 11 in the region below the frontside 101 against an implantation with dopants of the second type. Withinthe trench 15, the protective layer 31 at the trench sidewalls 151protects the first semiconductor zone 11 against a doping with dopantatoms of said second type.

Preferably, prior to carrying out the implantation step, a screen oxide32 is applied to the trench bottom 152, but it may, in particular, alsobe deposited over the whole area. Said screen oxide 32 serves forscattering the dopant atoms implanted for the production of the firstconnection zone 16.

In the example illustrated, the protective layer 31 is a layer dopedwith dopant atoms of the first type. In the course of carrying out athermal process, in which the semiconductor body 100 is heated to apredetermined diffusion temperature for a predetermined time duration atleast in the region of the first semiconductor zone 11, said dopantatoms of the first type indiffuse from the protective layer 31 into thefirst semiconductor zone 11, where they produce a second connection zone17, which is of the same conduction type as the first semiconductor zone11, but is doped more highly. The temperature of this diffusion processis between 800° C. and 1100° C. for a duration of between 10 seconds and15 minutes. The duration is dependent, inter alia, on the choice ofdopant. Whereas boron and phosphorus, for example, diffuse comparativelyrapidly, with the result that a shorter diffusion duration is to be set,arsenic diffuses comparatively slowly and requires longer diffusiondurations.

In order to produce the first connection zone 16, after the implantationof the dopant atoms of the first type, a thermal step is likewiserequired in order to anneal irradiation damage and to activate theimplanted dopant atoms, that is to say incorporate them into the crystallattice of the semiconductor body 100. Depending on which elements areused as dopant atoms of the first type and as dopant atoms of the secondtype, a single thermal step may be sufficient both for activating theimplanted dopant atoms of the second type and for indiffusing the dopantatoms of the first type from the protective layer 31 into the firstsemiconductor zone 11. If the diffusion temperature of the dopant atomsof the first type which serve for producing the second connection zone17 should be higher than the activation temperature required foractivating the dopant atoms of the second type, there is the possibilityof carrying out, prior to the implantation of the dopant atoms of thesecond type, a thermal step by means of which the dopant atoms of thefirst type are implanted into the first semiconductor zone 11. Onlyafterward are the dopant atoms of the second type implanted andactivated by means of a further thermal step in order to produce thesecond connection zone 16. The activation temperatures lie within therange of the above-mentioned diffusion temperatures (800° C. to 1100°C.). The activation durations may lie within the range of theabove-mentioned diffusion durations (15 seconds to 15 minutes).

The protective layer 31 with the dopant atoms of the first typecontained therein may be an electrically conductive layer, such as, forexample, doped polysilicon, but may also be an electrically insulatinglayer, such as, for example, a silicate glass. By way of example,polysilicon doped with arsenic or phosphorus, or else phosphosilicateglass (PSG) or arsenosilicate glass (ASG) is suitable for producing ann-doped second connection zone 17. For producing a p-doped secondconnection zone 17, polysilicon doped with boron or borosilicate glass(BSG) is suitable as the protective layer 31.

The screen oxide layer 32 not only serves for scattering the dopantatoms implanted into the trench bottom 152 but also has the function ofpreventing, during the diffusion method, dopant atoms of the first typefrom passing from the protective layer 31 into the atmosphere prevailingin the trench and from indiffusing from said atmosphere into the trenchbottom 152, where they would reduce the net doping of the firstconnection zone 16 with dopant atoms of the second conduction type andthus increase the contact resistance between said first connection zone16 and the connection electrode yet to be produced.

After the production of the first and second connection zones 16, 17 andprior to the production of said connection electrode 34, the screenoxide layer 32 is removed, for example by means of an etching method. Ifthe material of the protective layer 31 is a dielectric material, suchas, for example, silicate glass, said protective layer 31 must likewisebe removed, whereas an electrically conductive protective layer 31, suchas, for example, doped polysilicon, can remain.

FIG. 1 f shows the component after method steps for removing the screenoxide 32 and for producing a connection electrode 34. In this case, theprotective layer 31, which is an electrically conductive layer 31 in theexample illustrated, remains on the sidewalls 151 of the trench. Theconnection electrode 34 is produced by applying an electrode layer tothe sidewalls and the bottom of the trench, the trench 15 preferablybeing completely filled with electrode material. Prior to the depositionof the electrode layer, a barrier layer 33 is preferably applied, whichbarrier layer is electrically conductive and comprises titanium (Ti) forexample. Said barrier layer may fulfill various functions: thus, thebarrier layer 33 may protect the semiconductor material in the trenchagainst contamination during the production processes for the productionof the connection electrode 34. This is necessary particularly when aconnection electrode made of tungsten (W) is produced. Furthermore, thebarrier layer 33 may fulfill the function of a contact layer whichshort-circuits the connection zones 16, 17 which are dopedcomplementarily with respect to one another. This contact function ofthe barrier layer is necessary for example when the connection electrode34 is produced from highly doped polysilicon. In the case of producingthe connection electrode from an aluminum-copper compound, the barrierlayer prevents “spiking”.

A barrier layer may be dispensed with if AlCu(Si), for example, is usedas material for the connection electrode.

The result of the production method explained above is a semiconductorcomponent comprising a first and a second semiconductor zone 11, 12,which are doped complementarily with respect to one another and withwhich low-resistance contact is made by means of a connection electrode34. The low-resistance contact becomes possible by means of the twohighly doped connection zones 16, 17 and, in the region of the firstsemiconductor zone 11, by means of the highly doped protective layer 31,comprising polysilicon for example.

FIG. 2 shows a cross section through the component after the productionof the connection electrode 34 and the optional barrier layer 33, herethe protective layer having been removed at the sidewalls of the trench.The removal of the protective layer 31 may be effected for exampletogether with the removal of the screen oxide layer (32 in FIG. 1 e).Customary etching materials which are suitable for etching the screenoxide layer 32 usually also etch silicate glass, which is appropriate asprotective layer, so that the screen oxide layer 32 and the protectivelayer 31 are removed in a common method step. In the case of thecomponent illustrated in FIG. 2, the connection electrode comprising theoptional barrier layer 33 and the electrode layer 34 directly makescontact with the highly doped second connection zone 17 in the region ofthe sidewalls of the trench.

A further method for producing a connection electrode which makescontact with the first and second semiconductor zones 11, 12 with theuse of a protective layer is explained below with reference to FIGS. 3 ato 3 c.

Referring to FIG. 3 a, in this method, after the production of thetrench 15, a metallic protective layer 41 is applied to the sidewalls151 of the trench 15. The production of said metallic protective layer41 is effected for example according to the production of the protectivelayer 31 illustrated in FIG. 1 d by the deposition of a metallic layer41′, which is also illustrated in dashed fashion in FIG. 3 a, andsubsequent anisotropic etching back of said metallic layer 41′, with theresult that a protective layer 41 remains at the sidewalls 151 of thetrench 15.

Referring to FIG. 3 b, subsequently, a dopant material 43 containingdopant atoms of the second type is introduced into the trench 15. Saidmaterial 43 containing dopant atoms is doped polysilicon, for example.Said dopant material 43 must at least partly fill the trench, so thatthe bottom 152 of the trench is covered, although this dopant materiallayer may also be deposited in such a way that the trench 15 iscompletely filled with dopant material 43 and that regions of thisdopant material layer 43 are also arranged above the front side of thesemiconductor body 101 as well, as is illustrated in FIG. 3 b.

The production of said dopant material layer 43 is followed by adiffusion step, in which the semiconductor body 100 is heated to adiffusion temperature for a predetermined time duration, so that dopantatoms indiffuse from the dopant material layer 43 at the bottom 152 ofthe trench into the second semiconductor zone 12, where they produce ahighly doped first connection zone 16 of the second conduction type. Theprotective layer 41 at the trench sidewalls 151 serves as a diffusionbarrier and protects the first semiconductor zone 11 during thediffusion method against an indiffusion of dopant atoms of the secondconduction type into said first semiconductor zone 11. In the boundaryregion between the protective layer 41 and the semiconductor material, ametal-semiconductor compound arises during the diffusion process andensures a low-resistance connection contact between the metallicprotective layer 41 and, in particular, the first semiconductor zone 11.When silicon is used as semiconductor material, said metal-semiconductorcompound is a silicide. Titanium, in particular, is suitable as materialfor the metallic protective layer.

After the production of the connection zone 16 below the trench bottomin the second semiconductor zone 12, the dopant material layer 43 isremoved, for example by means of an etching method. The connectionelectrode 34 is subsequently produced by depositing an electrodematerial layer onto the sidewalls 151 and the bottom 152 of the trench15, a barrier layer 33 optionally being applied at least to the trenchbottom 152 and the sidewalls 151 of the trench prior to the depositionof the electrode layer. The dopant material layer may comprise anelectrically conductive material, such as, for example, dopedpolysilicon. In a manner not illustrated in any greater detail, such anelectrically conductive dopant material layer may remain at least insections in the trench and fulfill the function of the connectionelectrode there. There is thus the possibility, for example, of etchingback such an electrically conductive dopant material layer after theindiffusion of the dopant atoms into the semiconductor body 100 to anextent such that the is still at least partly filled with the dopantmaterial layer, and of subsequently producing an electrode layer, forexample made of aluminum, which forms a further part of the connectionelectrode and makes contact with the dopant material layer.

Such an electrode layer may also be applied to the dopant material layer34 illustrated in FIG. 3 c directly, that is to say without a previousetching process, if said layer comprises an electrically conductivematerial.

FIGS. 4 a to 4 c explained below show a modification of the methodexplained above with reference to FIGS. 3 a to 3 c. In this method,after the production of the trench 15, a metallic protective layer 42 isapplied to the trench bottom 152, while the trench sidewalls remainfree. The protective layer 42 comprises for example a silicide, such astitanium silicide or cobalt silicide. Such a protective layer may beproduced by highly nonconformal sputtering of a metal, such as titaniumor cobalt, and a subsequent nonconformal self-aligned TiSi process.During this nonconformal deposition by sputtering, the metal is appliedto the bottom 151 of the trench 15 and to the insulation layer 23, butnot to the sidewalls 152 of the trench. A thermal process issubsequently carried out, by means of which the metal at the trenchbottom 151 reacts with the silicon of the semiconductor body 100 to forma silicide and forms the protective layer there, while the metal on theinsulation layer does not react. The metal remaining on the insulationlayer 23 is subsequently removed wet-chemically.

After the production of this protective layer 42 at the trench bottom152, the trench 15 is filled at least as far as an upper edge of thesecond semiconductor layer 11, but preferably completely, with a dopantmaterial layer 44 having dopant atoms of the same conduction type as thefirst semiconductor zone 11, that is to say dopant atoms of the firsttype. Said dopant material layer 44 is a doped polysilicon layer, forexample. After the production of said dopant material layer 44, adiffusion process is effected, in which the semiconductor body is heatedto a diffusion temperature for a predetermined time duration, as aresult of which dopant atoms indiffuse from the dopant material layer 44via the sidewalls 152 of the trench 15 into the first semiconductor zone11, where they form a highly doped connection zone 17 of the sameconduction type as the first semiconductor zone 11. The dopant atoms arephosphorus atoms or arsenic atoms, for example, if an n-doped connectionzone 17 is to be produced, and the dopant atoms are boron atoms, forexample, if a p-doped connection zone 17 is to be produced.

After the conclusion of the diffusion method, the dopant material layer44 is removed and an electrode material is applied to the sidewalls andthe bottom of the trench, or the trench is completely filled with anelectrode material, as is illustrated as the result in FIG. 4 c. Abarrier layer 33, for example made of titanium, is optionally applied atleast to the sidewalls and the bottom of the trench prior to thedeposition of the electrode layer 34.

An alternative method for producing a connection electrode which makescontact with the first and second semiconductor zones 11, 12 isexplained below with reference to FIGS. 5 a to 5 d.

Referring to FIG. 5 a, this method involves firstly producing a trench15′ extending through the dielectric layer 23 via the front side 101down to a first trench depth d1 into the semiconductor body 100, saidfirst trench depth d1 being smaller than the ultimately desired depth ofthe trench. In the example in FIG. 5 a, this first trench section 15′extends right into the second semiconductor zone 12, but may—in a mannernot specifically illustrated—also end above said second semiconductorzone 12 in the first semiconductor zone 11.

Said first trench section 15′ has sidewalls 151′ and a bottom 152′.Referring to FIG. 5 d, dopant atoms are introduced via the sidewalls151′ and the bottom 152′ into the first and second semiconductor zones11, 12 in order to produce a highly doped connection zone of the sameconductivity type as the first semiconductor zone 11. For this purpose,dopant atoms of the first type are implanted into the firstsemiconductor zone 11 via the sidewalls 151′, for example. In this case,the dopant atoms are also implanted into the second semiconductor zone12 via the bottom 152 of the trench 15′. The semiconductor regionarranged adjacent to the sidewalls 151 and the bottom 152 of the trenchand having dopant atoms of the first type implanted therein isdesignated by the reference symbol 17′ in FIG. 5 b. For carrying outthis implantation method, a screen oxide 32 is optionally applied atleast to the sidewalls 151′ and the bottom 152′ of the trench 15.

Instead of carrying out an implantation method, the doped semiconductorzone 17′ may also be produced by means of a diffusion method by thetrench section 15′—in a manner that is not specificallyillustrated—being filled with a material containing dopant atoms and bydopant atoms subsequently being indiffused from said material into thefirst and second semiconductor zones 11, 12 during a thermal step.

During next method steps, the result of which is illustrated in FIG. 5c, the trench is etched in the direction of the second semiconductorzone 12 down to a desired end depth d2 by means of an etching method. Ifa screen oxide 32 was applied for the method steps explained withreference to FIG. 5 b, said screen oxide is firstly removedanisotropically from the bottom 152′ of the trench section 15′, whereassaid screen oxide remains—in a manner not specifically illustrated—onthe sidewalls 151′ of the trench section 15′. In this case, the furthertrench section which is produced by the etching method and extendsfurther into the semiconductor body proceeding from the bottom 152′ ofthe first trench section 151 has a smaller width w2 than the firsttrench section 15′, which has a width w1.

After the trench has been lengthened down to its desired end depth d2,dopant atoms are implanted into the second semiconductor zone 12 via thebottom 152 of the trench 15 in order to produce a highly dopedconnection zone 16 of the same conduction type as the secondsemiconductor zone 12. After the implantation of these dopant atoms, athermal step is required, in a manner already explained, in order toanneal irradiation damage and to activate the implanted dopant atoms. Inthis case, a common thermal step may be sufficient for activating thedopant atoms of the first type implanted into the region 171 and foractivating the dopant atoms of the second type implanted via the bottom152 of the trench. As a result, this gives rise to a highly dopedconnection zone 16 of the same conduction type as the secondsemiconductor zone 12 at the bottom of the trench produced in two stagesand a highly doped connection zone 17 of the same conduction type as thefirst semiconductor zone 11 at sidewalls of the initially producedtrench section 151 of the trench produced in two stages.

These method steps for producing the connection zones 16, 17 arefollowed by method steps for producing the connection electrode. Theresult of these method steps is illustrated in FIG. 5 d. For producingthe connection electrode, as in the method already explained previously,an electrode layer is deposited onto the sidewalls and the bottom of thetrench, the trench preferably being completely filled with electrodematerial. Furthermore, a barrier layer 33 may optionally be producedonto the sidewalls and the bottom of the trench prior to the depositionof the electrode layer.

A further alternative of a method for producing a connection electrodewhich makes contact with the first and second semiconductor zones 11, 12is explained below with reference to FIGS. 6 a to 6 c. Referring toFIGS. 6 a and 6 b, this method provides for implanting dopant atoms ofthe first conduction type via the sidewalls 151 of the trench 15 intothe first semiconductor zone 11 and dopant atoms of the second type viathe bottom 152 of the trench into the second semiconductor zone, inorder thereby to produce a highly doped connection zone 17 of the sameconduction type as the first semiconductor zone 11 in said semiconductorzone 11 and to produce a highly doped connection zone of the sameconduction type as the second semiconductor zone in said secondsemiconductor zone 12. For carrying out these implantation steps, ascreen oxide 32 is preferably applied at least to the sidwalls 151 andthe bottom of the trench 152.

In order to ensure that the dopant atoms of the first type for theproduction of the connection zone 17 are essentially introduced onlyinto the first semiconductor zone II, an implantation angle at which thedopant atoms are implanted is chosen such that no dopant atoms can passas far as the trench bottom 152. In this case, given a suitableimplantation angle, the upper edges of the trench 15 shield the trenchbottom against an implantation of dopant atoms of the first type. Givena trench depth d and a trench width w, the following holds true for thesmallest angle a at which the dopant atoms are still just permitted tobe implanted relative to the vertical so as not to pass as far as thetrench bottom:

α=arctan(w/d)

When a screen oxide 32 is provided, d designates the trench depth stillpresent after the application of the screen oxide, while w designatesthe width of the trench that is present after the application of thescreen oxide 32.

In order to avoid an implantation of dopant atoms into the bottom of thetrench, the sidewall implantation is thus effected at angles which areless than the limiting angle α specified in equation 1.

The production of the connection zone 16 below the trench bottom 152 iseffected by implantation of dopant atoms at an angle of 0° relative tothe vertical, that is to say relative to the trench sidewalls 151, or atan angle of 90° relative to the trench bottom. This implantationprevents dopant atoms from being implanted into the first semiconductorzone 11 via the sidewalls 151 of the trench.

It generally holds true that, in the case of the method explained above,the limiting angle α—and thus the angles at which the dopant atoms ofthe first type for the production of the connection zone 17 arepermitted to be implanted—may be smaller, the higher the aspect ratio ofthe trench, that is to say the ratio of trench width to trench depth.Whereas in the case of an aspect ratio of 1:1 the implantation angleshould lie between 45° and 60° in order to ensure that no dopant atomsare implanted into the bottom of the trench, in the case of an aspectratio of 3:1 angles of between 20° and 45° already suffice to ensurethis.

The implantation methods are followed by the method steps alreadyexplained above for producing the connection electrode, in which case ascreen oxide 32 that was possibly applied is removed prior to theproduction of said connection electrode.

FIG. 6 c shows the component after the method steps for producing theconnection electrode 34 have been carried out, a barrier layer 33optionally being applied at least to the sidewalls and to the bottom ofthe trench 15 prior to the deposition of the electrode layer forproducing the connection electrode.

A possible method for producing the trench 15 that extends into thesemiconductor body 100 proceeding from the front side 101 for the laterconnection electrode is explained below with reference to FIGS. 7 a to 7e.

FIG. 7 a shows the semiconductor body 100 in side view in cross sectionafter the performance of method steps for producing the gate electrodes21 arranged in trenches and the gate dielectric layers 22 whichdielectrically insulate the gate electrodes 21 from the semiconductorbody 100 and after the production of the second semiconductor layer 12.Said second semiconductor layer 12 is produced for example by implantingdopant atoms of the second conduction type via the front side 101 intothe semiconductor body 100 and subsequently carrying out a thermaltreatment. In this case, the first semiconductor zone 11 may be producedin a manner corresponding to the second semiconductor zone byimplantation of dopant atoms and a subsequent thermal treatment directlyafter the production of the second semiconductor zone 12, but may—aswill be explained below—also be produced at a later point in time in themethod.

In this arrangement, the gate electrodes 21 are realized in such a waythat an upper end of the gate electrodes 21 is recessed relative to thefront side 101 of the semiconductor body 100, with the result thatcut-outs 18 are in each case present above the gate electrodes 21 in thesemiconductor body 100.

Referring to FIG. 7 b, the arrangement illustrated in FIG. 7 a issubjected to a thermal treatment, resulting in the oxidation of sectionsof the semiconductor body 100 and of the gate electrodes 21 that arenear the surface, as a result of which an oxide layer 24′ arises in theregion of the front side 101 both above sections of the semiconductorbody 100, in particular above the mesa regions, and above the gateelectrodes 21. The gate electrodes 21 comprise doped polysilicon, forexample, and thus oxidize approximately at the same temperatures as thesemiconductor body 100, comprising silicon for example.

A thickness of the oxide layer is between 200 and 300 nm, for example,for which a layer of the semiconductor body near the surface with athickness of approximately 100 to 150 nm is “consumed”. In this case,the oxidation of the semiconductor body 100 is effected both at thefront side 101 and in those regions which are uncovered laterally at thecut-outs 18 above the gate electrodes 21. This oxidation of the frontside 101 and of the sidewalls of the cutouts has the effect that theoxide layer 24′ runs in a funnel-shaped or V-shaped manner above thegate electrodes 21. The oxidation layer 24′, which grows everywhere onuncovered regions of the semiconductor body 100 and of the gateelectrodes 21, due to the cut-outs 18 above the gate electrodes 21,thereby has an uneven surface structure with depressions above the gateelectrodes 21.

Referring to FIG. 7 c, a filling layer 25′ is subsequently applied tothe oxide layer 24′, and fills the cut-outs of the oxide layer 24′. Saidfilling layer 25′ comprises for example an insulation material, forexample a deposited oxide, such as tetraethoxysilane (TEOS), or a dopedor undoped silicate glass (PSG, BPSG, USG).

Said filling layer 25′ and the oxide layer 24′ are subsequently removeduntil the mesa region of the semiconductor body 100 that is situatedbetween the trenches having the gate electrodes 21 is uncovered, whichis illustrated as the result in FIG. 7 b. These two layers are removedfor example by means of a chemical mechanical polishing method (CMP) orby means of an etching method. In this case, the oxide layer 24′ and thefilling layer 25′ remain in sections in the region of the earliercut-outs (18 in FIG. 7 a) of the semiconductor body 100 above the gateelectrodes 21. It should be noted in this connection that the fillinglayer 25′ essentially serves for completely filling said cut-outs abovethe gate electrodes 21. The deposition of said filling layer 25′ may bedispensed with when a thickness of the oxide layer 24′ is chosen suchthat the latter already fills the cut-outs as far as the front side 101of the semiconductor body 100, that is to say if a surface of the oxidelayer 24′ in a region above the gate electrodes 21, in the verticaldirection, is situated higher than the front side 101 of thesemiconductor body 100 in the region of the mesa region.

Sections 24, 25 of the oxide layer 24′ and of the filling layer 25′ thatremain after the removal process has been carried out form “plugs” ofinsulation material above the gate electrodes 21, said “plugs” wideningin the direction of the front side 101 of the semiconductor body. If thefirst semiconductor zone 11 has not already been produced after theproduction of the second semiconductor zone 12, said first semiconductorzone can be implemented by employing an implantation and thermal processafter the production of the insulation plugs 24, 25.

An etching method is subsequently carried out using said insulationplugs 24, 25 as a mask, by means of which etching method a trench 15extending through the first semiconductor zone 11 right into the secondsemiconductor zone 12 proceeding from the front side 101 is etched intothe mesa region. The etching method is an anisotropic etching methodthat removes the semiconductor material exclusively in the verticaldirection of the semiconductor body 100. In this case, the dimensions ofthe trench 15 in the lateral direction are determined by the mutualspacings of insulation plugs 24, 25 in the lateral direction in theregion of the front side 101 of the semiconductor body 100.

Since the insulation plugs widen in the direction of the front side 101of the semiconductor body and thus in the lateral direction go beyondthe dimensions of the trenches having the gate electrodes 21 arrangedtherein, said insulation plugs 24, 25 act as spacers between thetrenches having gate electrodes 21 and the trench 15 produced by theanisotropic etching for the later connection electrode. In this case,the distance between the trenches having the gate electrodes 21 and thetrench 15 for the connection electrode is essentially determined by thethickness of the oxide layer 24.

In order to ensure that a highly doped first connection zone (16 inFIGS. 1 to 6) produced below the trench bottom 152 in the secondsemiconductor zone 12 is at a sufficiently large distance in the lateraldirection from the gate dielectric 22, so that said connection zone doesnot influence the channel properties of the MOS transistor, it isdesirable to make the distance between the trench having the gateelectrode 21 and the trench 15 for the connection electrode as large aspossible. In the case of the method for producing said trench 15explained above with reference to FIG. 7, however, said distance islimited by the thickness of the oxide layer 24′, which cannot berealized with an arbitrary thickness in order to limit mechanicalstresses in the component structure, which increase as the thickness ofthe oxide layer 24′ increases.

One possibility for setting the distance between the highly dopedconnection zone in the second semiconductor layer 12 and the gatedielectric 22 in the lateral direction independently of the distancebetween the trench 15 and the trench having the gate electrode 21consists in producing the connection zone 16 using the method explainedwith reference to FIG. 3. In this method, a protective layer 41 isapplied to sidewalls of the trench 15, which protective layer limits theimplantation region at the trench bottom 152 in the lateral directionwhen carrying out the implantation method for producing the connectionzone 16.

A further method for producing a highly doped connection zone in thesecond semiconductor layer 12, which makes it possible to set thedistance between said connection zone and the trench having the gateelectrode 21 independently of the distance between the trench having thegate electrode 21 and the trench 15 for the connection electrode, isexplained below with reference to FIGS. 8 a to 8 c.

Referring to FIG. 8 a, this method involves firstly producing a spacerlayer 51, which is deposited onto the component arrangement over thewhole area, by way of example. Said spacer layer 51 is for example alayer made of a deposited oxide (TEOS) or a nitride layer. Furthermore,said spacer layer 51 may also have a plurality of partial layers, forexample an oxide layer 51A deposited first and a nitride layer SIBdeposited afterward, which is illustrated in dashed fashion in FIG. 8 a.

Referring to FIG. 8 b, an implantation method is subsequently carriedout, by means of which dopant atoms of the second conduction type areimplanted through the spacer layer 51 via the trench bottom 152 into thesecond semiconductor layer 12. In this case, the insulation plugs 24, 25prevent an implantation of dopant atoms into regions of thesemiconductor body which are arranged adjacent to the trench 15 in thelateral direction. At the sidewalls 151 of the trench I5, the spacerlayer 51 prevents an implantation of dopant atoms of the secondconduction type into the first semiconductor layer 11. While the dopantatoms in the region of the trench bottom 152 penetrate through thespacer layer perpendicularly, dopant atoms in the region of thesidewalls 151 of the trench can impinge on the spacer layer 51 at mostat a very shallow angle at which, however, they cannot penetrate throughthe spacer layer 51. Consequently, in this method, the spacer layer 51acts as a protective layer that prevents doping of the mesa region inthe region of the sidewalls 151 of the trench 15. The spacer layerfurthermore limits the implantation region, that is to say the region inwhich dopant atoms are implanted, in the lateral direction in the regionof the trench bottom 152. In this case, the thickness of the spacerlayer 51 serves for setting the distance between said implantationregion, and thus the highly doped connection zone 16 produced by theimplantation, and the trench having the gate electrode 21.

For setting the distance between the highly doped connection zone 16 andthe gate electrode 21, it suffices to produce the spacer layer 51 at thesidewalls 151 of the trench 15. Referring to FIG. 9, there is optionallythe possibility, therefore, of anisotropically etching back the spacerlayer 51, that is to say removing it from the trench bottom 152, inparticular, prior to carrying out the implantation method.

Referring to FIG. 8 c, which shows the component structure after furthermethod steps have been carried out, the spacer layer 51 is removed afterthe production of the highly doped connection zone 16 and the trench 15is filled with an electrode material for producing the connectionelectrode in the manner already explained, in which case, in the manneralready explained, said connection electrode may have two partiallayers, namely a barrier layer 33 and an electrode layer 34. There isoptionally the possibility of producing a highly doped connection zone17 in the first semiconductor layer 11 prior to producing the connectionelectrode 33, 34. Said highly doped connection zone 11 may be producedfor example by means of an implantation—explained with reference to FIG.6 a—of dopant atoms of the first conduction type at an angle inclinedrelative to the perpendicular.

1. A method for producing a connection electrode for a firstsemiconductor zone and a second semiconductor zone, which are arrangedone above another and are doped complementarily with respect to oneanother, the method comprising: producing a trench extending through thefirst semiconductor zone into the second semiconductor zone in such away that the first semiconductor zone is uncovered at sidewalls of thetrench and the second semiconductor zone is uncovered at least at abottom of the trench, producing a first connection zone in the firstsemiconductor zone by implanting dopant atoms into the sidewalls atleast at a first angle relative to the sidewalls, and is performed afterthe trench has been produced, producing a second connection zone in thesecond semiconductor zone by implanting dopant atoms at least at asecond angle, which is different from the first angle, relative to thesidewalls, depositing an electrode layer at least onto the sidewalls andthe bottom of the trench for the purpose of producing the connectionelectrode.
 2. The method as claimed in claim 1, wherein, prior to theproduction of the electrode layer, a barrier layer is applied to thesidewalls and the bottom of the trench.
 3. The method as claimed inclaim 2, wherein, prior to producing the first connection zone, a screenlayer is applied to the sidewalls and the bottom of the trench.
 4. Themethod as claimed in claim 1, wherein the first angle relative to thesidewalls is greater than the second angle relative to the sidewalls. 5.The method as claimed in claim 4, wherein, prior to the production ofthe electrode layer, a barrier layer is applied to the sidewalls and thebottom of the trench.
 6. The method as claimed in claim 4, wherein,prior to producing the first connection zone, a screen layer is appliedto the sidewalls and the bottom of the trench.
 7. The method as claimedin claim 6, wherein, prior to the production of the electrode layer, abarrier layer is applied to the sidewalls and the bottom of the trench.8. The method as claimed in claim 1, wherein, prior to producing thefirst connection zone, a screen layer is applied to the sidewalls andthe bottom of the trench.